Nutrition is one of the cornerstones of health, well-being, and the prevention and treatment of numerous chronic diseases. Nutritional products play an important role in these areas and attempts to provide cost-efficient, readily available and convenient nutritional products to the general public and those with special dietary needs has been a major focus in recent years. Complete nutritional products, i.e. those which contain all the essential macro and micro nutrients, have heretofore been available only in sterilized products or frozen products. Sterilized products are generally sold in hermetically sealed containers such as cans and are intended to have a long room temperature shelf-life. Table 2 lists many commercially available sterilized nutritional products. Such products require expensive processing steps which must be carefully controlled to properly remove microorganisms and bacterial enzymes. As will be discussed further herein, sterilization processes, due to the severity of the heat treatment can cause undesirable physical, chemical, enzymatic and microbial changes which deleteriously affect the final product. Moreover, although such sterilized products are often marketed as "ready-to-drink", they are typically stored at room temperature and therefore require refrigeration for maximum taste. Moreover, enzymatic reactions still occur, albeit slower, during room temperature storage of sterilized products. Such reactions can result in a host of undesirable defects, such as the destruction of vitamins which are necessary to the integrity of the overall product. Since sterilized products are designed to have up to one and a half year of room temperature shelf-life, such a product will have a different actual content of degradable micro nutrients (vitamins) in the early part of its shelf-life as compared to the latter part. Thus, a consumer will obtain a different and unknown amount of vitamins depending on when the sterilized product is consumed. To account for this slow degradative process during long-term shelf-life, manufacturers of sterilized complete nutritional products often include up to 50% more of a given vitamin than would normally be included to account for the inherent degradation loss and to ensure the product is likely to contain at least the labeled amount of nutrients at the end of its shelf-life. Such large overdosing results in an imbalance in the taste of the product, particularly if consumed in the early stages of its shelf-life. Moreover, the cost factor of including such large overdoses is enormous. In addition to the high cost of sterilization, and increased overdosing of vitamins, sterilization processes require high cost packaging, such as in metal cans and room-temperature self-stable laminated packages such as TetraBric.RTM. & Combibloc.RTM..
In addition to sterilized complete nutritional products, there are several frozen ultra-pasteurized or pasteurized complete nutritional products which are commercially available. These are set forth in Table 3. Frozen products cannot truly be considered ready-to-drink at the point of purchase because they require thawing before consumption.
More importantly, however, the freezing and thawing process has a number of known deleterious affects on complex compositions which have a variety of sensitive components contained therein. For example, upon freezing and thawing of a complex nutritional composition such as those of the present invention, a series of physical-chemical reactions can occur in the product. Phase separation, and the resultant unpleasant appearance is a common problem. Additionally, proteins can become denatured and precipitate out during the thawing process. Such precipitate is not only undesirable from an appearance point of view to the consumer, but also has unwanted texture and mouthfeel characteristics. Flavors, vitamins and minerals can become physically entrapped in the precipitate complex. It is common for consumers to drink only the liquid phase of a beverage and ignore the undesired solid phase which precipitates out. As a result, the consumer is effectively deprived of the very nutrients for which the composition is designed to deliver. The result is a product which is ineffective at meeting its intended function and the needs of the consumer or patient.
Moreover, frozen products require the extra steps of freezing during processing, require special handling during distribution and special storage systems as well. Frozen products generally need to be thawed in a refrigerator for 24 hours prior to use. Other products which are not frozen, such as modified milks and milk substitutes, are commercially available but are nutritionally incomplete from the vitamin and mineral point of view.
Like milk, liquid nutritional products (usually containing milk proteins) are heated for a variety of reasons, the main reasons being: to remove potential pathogenic organisms and to increase shelf-life. The major concerns about the resulting products of thermal process are safety and quality. Like milk, heat-treated nutritional products should not be a public heath risk. They should have a good keeping quality, provide an intended balance of nutrients, and be of desirable sensory characteristics, i.e., appearance, color, flavor, and mouth feel. When milk or nutritional products are heated at a constant temperature, all their constituents and components will be affected, but to different extents. Increasing the temperature will accelerate reaction rates. But different reactions will be affected to different extents. Physical, chemical, enzymatic and microbial changes will depend principally upon the time-temperature conditions, but will also be influenced by other factors, such as composition, pH, and oxygen content. The wide range of reactions taking place when nutritional products are heated will influence the safety and quality of the product. Upon heating of products at higher temperatures for longer times, some undesirable changes can also take place (e.g., decrease in pH, Maillard browning, cooked caramel flavor, denaturation of whey proteins and interaction with casein). The changes that take place during heating and subsequent storage, can affect the nutritional value and sensory characteristics.
In thermal processing, the most important parameter is the level of microbial inactivation achieved. For safety reasons, the minimum holding time (residence time) should be considered for microbial inactivation, although this will give an underestimate of the true level of microbial inactivation.
In terms of microbial quality and reducing spoilage rates, the emphasis is toward that of prevention. One approach, now widely used, is that of Hazard Analysis Critical Control Points (HACCP). Here the philosophy is to identify where hazard may occur from raw materials, different processing stages, packaging, or subsequent handling and storage. Critical control points are then established. These are points in the production process where the hazard can be effectively controlled. Loss of control permits the realization of the potential hazard as an unacceptable food safety or spoilage risk.
The quality of raw materials (ingredients) also has a pronounced effect on the quality of the final product. From the microbial point of view, the ingredients must be free of serious pathogens, and have initial total bacterial counts not more than 104 per gram. This reflects good hygiene in production of the ingredients. It is also useful to monitor psychotropic bacteria in raw ingredients (via direct assay of proteolytic enzymes) as they are usually predominant among the microorganisms found in pasteurized products.